Qjet accelerator pump

[cruiserman]

My 72 GMC has sat over the winter, and I've been trying to get it started over the past few days. I finally got it running today, but it has troubles.

The carb on it is a rebuilt Qjet. I had to pump the crap out of the pedal to get it running after lots of cranking. If I put my hand over the air intake the idle speeds up. If I blip the throttle, it gasps for air, and there's hardly any power.

Sounds like bad acc pump?

thanks, eric

[72chevyk10]

i think acc pumps are for mechanicly puting fuel into the mixture when first geting on the throtle. sounds to me like a stuck float(?)

[Bus Ted Knuckle]

idle increasing when you cover the intake is indicative of a lean condition, possibly a vacuum leak. I don't think that it is your acc. pump.

check your filter(s) and post back if they are clear. The check ball being stuck is about the only way this could involve your accelerator pump.

It is possible that the carb may need to be cleaned out, being that it sat for a while. Gas turns into varnish fast these days.

[PanelDeland]

Was the gas stabilized when it was parked?As Bill said it may be varnish.The cranking and pumping are pretty normal since the fuel tend to evaporate out of the float bowl after time.It may be as simple as bad gas after sitting.

[chipflyer]

To simply test your accelerator pump with the engine shut off, remove the air cleaner, hold the choke open and watch for fuel to be sprayed into the primaries as you open the throttle by hand. If you see no fuel being sprayed you have an issue with the accelerator pump system.

Jeff

[luvmtrks4366]

Just my 2 cents. You might also check the throttle shaft for sloppiness. Alot of times with a rebuild, you have to rebush this or you may get a vacuum leak there also, even though it's rebuilt.

[Wrenchbender Ret]

Put a can of Sea-Foam in the gas tank. Open the idle jets up about a turn or 2 CCW. Run the engine a bit & slowly turn the idle jets in till the engine starts slowing down, then back them out about a 1/2 turn. If that doesn't cure it & you don't have vacuum leaks like previously suggested, the float level may be too low.

[cruiserman]

The float is set at 0.375". I checked the fuel squirt from the acc pump, and it's not good. The pump is new and looks good. Check ball is in place. If I ramp up the throttle it sounds OK. If I blip it, it will gasp for air. If I blip it with the intake covered, it does better. Maybe something stuck in the fuel passage from the pump?

A few notes:
* Vacuum from the port on the front driver's side of the carb only produces 8". Intake vacuum is 16.5" at the dual port near the distributor.
* timing is 10*BTDC base. with vac it's 15*, so I'm thinking it needs more vacuum. if i use the intake port, timing jumps way up. probably need to use that source and turn down the adjustable vac advance to 15* or so.
* 73/43b primary jets/rods. stock is 72/43b.

[Bus Ted Knuckle]

Originally Posted by cruiserman

The float is set at 0.375". I checked the fuel squirt from the acc pump, and it's not good. The pump is new and looks good. Check ball is in place. If I ramp up the throttle it sounds OK. If I blip it, it will gasp for air. If I blip it with the intake covered, it does better. Maybe something stuck in the fuel passage from the pump?

A few notes:
* Vacuum from the port on the front driver's side of the carb only produces 8". Intake vacuum is 16.5" at the dual port near the distributor.
* timing is 10*BTDC base. with vac it's 15*, so I'm thinking it needs more vacuum. if i use the intake port, timing jumps way up. probably need to use that source and turn down the adjustable vac advance to 15* or so.
* 73/43b primary jets/rods. stock is 72/43b.

it could very well be some varnish in any one of the passages in your carb. take it apart and blast with some carb cleaner, then blow down each hole with compressed air. I am sure it'll run fine after that.

[cruiserman]

I checked the pump squirt tonight, and it looks good now. Still have the gasping for air when the throttle is blipped.

Any concerns about only 8" of vacuum driving the vac advance?

[chipflyer]

You have found your problem if you are not getting a squirt from the accelerator pump.
Take the airhorn back off and re-seat the checkball. Do this by taking a small punch and lightly tapping the ball with a small hammer, not to hard, just a tap. After re-seating it fill the checkball cavity with wd40 and see if it leaks down, it should not. Make sure the accelereator pump moves up and down in the bore without sticking, the seal can actually stick and the shaft still go up and down. The photo is of one I am building that had Ethanol run through it, it destroys the accelerator pump seal.
Here is a link to Cliff Ruggles very good quadrajet forum, you might ask over there if you still have trouble.
http://www.cliffshighperformance.com...machinesforum/

[chipflyer]

Never mind about the pump, looks like you got it working now.

[67shortie]

Updates on this?

Also, just to confirm for my own curiosity, you mentioned the floats were set at .375? Is this 3/4 of an inch from the airhorn surface?

If so, your floats are set too low, should be 1/4" to 5/16ths from the airhorn surface measured from the top of the float. The floats set too low will cause a very lean condition like you are experiencing.

Your jet rod combo is a 30 which is plenty rich. What power piston spring are you using? If it's stock, and you said the engine vacuum is 16.5 your spring may be seated too long into the fuel curve causing a lean surge as well

I bought an Edelbrock q-jet pistion spring pack, helped me quite a bit dialing in mine.

[cruiserman]

Yes, the float is seat at 0.375" from the top of the body.

I don't know what spring is in there. You're saying it may be too weak?

[Wrenchbender Ret]

.375 is 3/8 in. It could be a little low depends on the carb. You need to take the number off the carb & match it to the speck sheet. You are probably hooking your vacuum gauge to ported vacuum. It will be lower then full manifold vacuum. The port on the manifold is the actual vacuum.

[cruiserman]

Going from lars grimsrud's listing, my carb came stock with 72/43b and DA secondary rods. Mine has 73/43b/DA.

I'm going to switch the vacuum source, but I suspect that won't help with the problem.

How about secondary air valve opening too soon?

[cruiserman]

I spent a little more time on it tonight. I switched the vac source to manifold vac and turned down the idle speed.

I removed the acc pump lever and didn't notice any difference when hitting the throttle. Same big hesitation.

Exhaust smells like gas. I turned the idle screws 2 turns out from 3. Still smells like gas.

It takes a lot of pumping to get it started, and it takes 3 cycles to get it to finally run.